Investigation of permanent magnet assisted synchronous reluctance machines for traction drives in high power flux weakening operation

Abstract

This paper presents an investigation of several rotor topologies for permanent magnet assisted synchronous reluctance machines. Electric drivetrains for hybrid and full electric vehicles request a wide constant power demand up to high rotational speeds in deep flux weakening operation. Therefore, different rotor geometries and two kinds of permanent magnet materials for this machine type are compared with regard to peak torque and maximum power capability at a limited machine volume. A key criteria for enabling deep flux weakening capability of permanent magnet assisted synchronous reluctance motors is the right choice of the machine's pre-magnetization level and the permanent magnet flux linkage. The focus is to prefer rare earth free magnet concepts and maximize the utilization of low cost ferrite magnets. Finally, because of the given volume constraints a high permanent flux linkage value can only be realized by a combination of ferrites and rare earth magnets to achieve both a high power capability and attractive product costs.